diff --git a/tryton/pyson.py b/tryton/pyson.py
index 5eaa0edadc..a79067a80c 100644
--- a/tryton/pyson.py
+++ b/tryton/pyson.py
@@ -95,6 +95,14 @@ class PYSON(object):
     def contains(self, k):
         return In(k, self)
 
+    def __repr__(self):
+        klass = self.__class__.__name__
+        return '%s(%s)' % (klass, ', '.join(map(repr, self.__repr_params__)))
+
+    @property
+    def __repr_params__(self):
+        return NotImplementedError
+
 
 class PYSONEncoder(json.JSONEncoder):
 
@@ -132,6 +140,10 @@ class Eval(PYSON):
         self._value = value
         self._default = default
 
+    @property
+    def __repr_params__(self):
+        return self._value, self._default
+
     def pyson(self):
         return {
             '__class__': 'Eval',
@@ -161,6 +173,10 @@ class Not(PYSON):
             assert isinstance(value, bool), 'value must be boolean'
         self._value = value
 
+    @property
+    def __repr_params__(self):
+        return (self._value,)
+
     def pyson(self):
         return {
             '__class__': 'Not',
@@ -181,6 +197,10 @@ class Bool(PYSON):
         super(Bool, self).__init__()
         self._value = value
 
+    @property
+    def __repr_params__(self):
+        return (self._value,)
+
     def pyson(self):
         return {
             '__class__': 'Bool',
@@ -209,6 +229,10 @@ class And(PYSON):
         assert len(statements) >= 2, 'must have at least 2 statements'
         self._statements = list(statements)
 
+    @property
+    def __repr_params__(self):
+        return tuple(self._statements)
+
     def pyson(self):
         return {
             '__class__': 'And',
@@ -251,6 +275,10 @@ class Equal(PYSON):
         self._statement1 = statement1
         self._statement2 = statement2
 
+    @property
+    def __repr_params__(self):
+        return (self._statement1, self._statement2)
+
     def pyson(self):
         return {
             '__class__': 'Equal',
@@ -285,6 +313,10 @@ class Greater(PYSON):
         self._statement2 = statement2
         self._equal = equal
 
+    @property
+    def __repr_params__(self):
+        return (self._statement1, self._statement2, self._equal)
+
     def pyson(self):
         return {
             '__class__': 'Greater',
@@ -352,6 +384,10 @@ class If(PYSON):
         self._then_statement = then_statement
         self._else_statement = else_statement
 
+    @property
+    def __repr_params__(self):
+        return (self._condition, self._then_statement, self._else_statement)
+
     def pyson(self):
         return {
             '__class__': 'If',
@@ -391,6 +427,10 @@ class Get(PYSON):
         self._key = key
         self._default = default
 
+    @property
+    def __repr_params__(self):
+        return (self._obj, self._key, self._default)
+
     def pyson(self):
         return {
             '__class__': 'Get',
@@ -433,6 +473,10 @@ class In(PYSON):
         self._key = key
         self._obj = obj
 
+    @property
+    def __repr_params__(self):
+        return (self._key, self._obj)
+
     def pyson(self):
         return {
             '__class__': 'In',
@@ -467,6 +511,11 @@ class Date(PYSON):
         self._delta_months = delta_months
         self._delta_days = delta_days
 
+    @property
+    def __repr_params__(self):
+        return (self._year, self._month, self._day,
+            self._delta_years, self._delta_months, self._delta_days)
+
     def pyson(self):
         return {
             '__class__': 'Date',
@@ -520,6 +569,15 @@ class DateTime(Date):
         self._delta_seconds = delta_seconds
         self._delta_microseconds = delta_microseconds
 
+    @property
+    def __repr_params__(self):
+        date_params = super(DateTime, self).__repr_params__
+        return (date_params[:3]
+            + (self._hour, self._minute, self._second, self._microsecond)
+            + date_params[3:]
+            + (self._delta_hours, self._delta_minutes, self._delta_seconds,
+                self._delta_microseconds))
+
     def pyson(self):
         res = super(DateTime, self).pyson()
         res['__class__'] = 'DateTime'
@@ -568,6 +626,10 @@ class Len(PYSON):
                 'value must be a dict or list or a string'
         self._value = value
 
+    @property
+    def __repr_params__(self):
+        return (self._value,)
+
     def pyson(self):
         return {
             '__class__': 'Len',